Relationship in "Select" not working as expect

[FrancescoTerrosi]

Package

filament/filament

Package Version

v5.x

Laravel Version

v12+

Livewire Version

v4

PHP Version

PHP 8.4

Problem description

Select with ->relationship handling doesn't work as I would expect.

In my resource I have the following:

`

         Select::make('partner_parent_id')

               ->relationship(name: 'parent', titleAttribute: 'name')

               ->label('Partner padre')

               ->preload()

                ->searchable()

                ->loadingMessage('Caricamento partner...'),

`

The "parent" relationship is a one-to-one relationship with the same table.
The scenario is the following: I need to create entities that may have a parent-child relationship. An entity may have 0 or 1 parent. I create the first entity without assigning a parent to it as there are none. Then, I create another entity and set the previously created entity as this one's parent.
The new entity is created correctly, however it also becomes its parent's parent.

Expected behavior

I would expect that the parent's entity 'parent_id' remains unset.

Steps to reproduce

1. Create Filament user
2. Go to /admin panel
3. Log in and create a new "Partner" from "Partner resource" (insert name only)
4. Create another "Partner" and set the 'partner_parent_id' field, labeled 'Partner padre' to the previously created entity
5. After creation, you will see that the previously created entity's parent is set to the newly created entity's id

Reproduction repository (issue will be closed if this is not valid)

https://github.com/FrancescoTerrosi/select-relationship-bug

Relevant log output

[Nicholasbell03]

HI @FrancescoTerrosi I have reviewed and can't confim this as a package issue, this is just an incorrect setup of the relationships in the Models.

The bug is caused by an incorrect relationship definition in the Partner model.

The parent() method currently uses HasOne, which tells Laravel "find a Partner whose partner_parent_id points to me." This is backwards, it actually describes finding children, not a parent.

When Filament saves the form using this relationship, it follows that definition and sets the foreign key on the wrong record, causing the circular reference you observed.

The fix is to change the parent() relationship from HasOne to BelongsTo:

public function parent(): BelongsTo                                                                                                                
  {                                                                                                                                                  
      return $this->belongsTo(Partner::class, 'partner_parent_id');                                                                                  
  }

This correctly tells Laravel "my partner_parent_id field points to my parent."

One small note: this is technically a one-to-many relationship (one parent can have many children), not one-to-one. But either way, BelongsTo is the correct relationship type when the foreign key is on the current model.

If you truly want it to be one-to-one you are missing a unique constraint in your DB migration to make the partner_parent_id unique, but in Laravel you would still use the belongsTo() relationship if the foreign key is on the current model.

I hope this helps.

[FrancescoTerrosi]

Dang, I can't believe I ignored the relationship in the model
Also, this actually should be a one-to-many and not a one-to-one as I wrote in the post. I must have been super tired.

Sorry for the useless issue and thanks for pointing me towards the right place to look.
I guess I must have been pissed by the other issue I posted, and the very late time didn't help.